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   <title> Zoltan Developer's Guide:  Adding Algorithms: How to handle memory</title>

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<h2>
Memory Management in Zoltan Algorithms</h2>
Zoltan uses a <a href="../ug_html/ug_util_mem.html">memory management
package</a> to simplify debugging of memory problems. 
It is strongly recommended that algorithm
developers use the routines in this package, such as 
<a href="../ug_html/ug_util_mem.html#Zoltan_Malloc"><b>ZOLTAN_MALLOC</b> </a>,
<a href="../ug_html/ug_util_mem.html#Zoltan_Calloc"><b>ZOLTAN_CALLOC</b> </a> and 
<b><a href="../ug_html/ug_util_mem.html#Zoltan_Free">ZOLTAN_FREE</a></b>, instead
of the standard C routines for most memory management.
<p>
Macros that simplify the <a href="dev_lb_types.html#ID alloc">allocation of global and local identifiers (IDs)</a>
are defined in <i>zz/zz_id_const.h</i>.  These macros are described in the 
<a href="dev_lb_types.html">ID Data Types</a> section.  The macros include
error checking for the allocations and, thus, their use is highly recommended.

<p>When a dynamic structure needs to be returned to the application,
special memory allocation routines are needed.&nbsp; For example, the import
and export lists of data to migrate are returned to an application from
<b><a href="../ug_html/ug_interface_lb.html#Zoltan_LB_Partition">Zoltan_LB_Partition</a></b>
and 
<b><a href="../ug_html/ug_interface_mig.html#Zoltan_Invert_Lists">Zoltan_Invert_Lists</a></b>.
There are two special routines for managing memory for such situations,
called <b><a href="#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b> and <b><a href="#Zoltan_Special_Free">Zoltan_Special_Free</a></b>.
Algorithms must use these functions to maintain compatibility with both
C and Fortran90 applications; these special routines manage memory in a
way that is compatible with both languages.
<p>Some load-balancing algorithms may contain persistent data structures,
that is, data structures that are preserved between calls to the load-balancing
routine. The <a href="dev_lb_structs.html"><b>Zoltan_Struct</b></a> structure contains a field 
<a href="dev_add_struct.html"><i>LB.Data_Structure</i></a>
for this purpose, allowing multiple Zoltan structures to preserve
their own decomposition data. The developer should write a function that
frees this data structure.&nbsp; Use <b>Zoltan_RCB_Free_Structure </b>as an
example.
<p>

<!------------------------------------------------------------------------->
<hr>
<a NAME="Zoltan_Special_Malloc"></a>
<hr>
int <b>Zoltan_Special_Malloc</b>(struct
<b><a href="dev_lb_structs.html#Zoltan_Struct">Zoltan_Struct</a></b>
*<i>zz</i>, void **<i>array</i>, int <i>size</i>, <b>ZOLTAN_SPECIAL_MALLOC_TYPE</b><i>type</i>);&nbsp;
<hr>
<p>The <b>Zoltan_Special_Malloc</b> routine allocates memory to be returned to the application by Zoltan (e.g., the result arrays
of 
<b><a href="../ug_html/ug_interface_lb.html#Zoltan_LB_Partition">Zoltan_LB_Partition</a></b>
and 
<b><a href="../ug_html/ug_interface_mig.html#Zoltan_Invert_Lists">Zoltan_Invert_Lists</a></b>).
Returned memory must be allocated by <b>Zoltan_Special_Malloc</b> to insure it is allocated
by the same language as the application. Memory allocated by <b>Zoltan_Special_Malloc</b>
must be deallocated by <b><a href="#Zoltan_Special_Free">Zoltan_Special_Free</a></b>.
<br>&nbsp;
<table WIDTH="100%" >
<tr VALIGN=TOP>
<td VALIGN=TOP WIDTH="20%"><b>Arguments:</b></td>

<td WIDTH="80%"></td>
</tr>

<tr>
<td VALIGN=TOP><i>&nbsp;&nbsp;&nbsp; zz</i></td>

<td>The Zoltan structure currently in use.</td>
</tr>

<tr>
<td VALIGN=TOP><i>&nbsp;&nbsp;&nbsp; array</i></td>

<td>
Upon return, a pointer to the allocated space.
Usually of type int** or <b><a href="dev_lb_types.html">ZOLTAN_ID_PTR</a></b>*.
</td>
</tr>

<tr>
<td VALIGN=TOP><i>&nbsp;&nbsp;&nbsp; size</i></td>

<td>The number of elements (not bytes) to be allocated.</td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp;&nbsp; <i>type</i></td>

<td>The type of array to allocate. Must be one of <b>ZOLTAN_SPECIAL_MALLOC_INT</b>,
<b>ZOLTAN_SPECIAL_MALLOC_GID</b>
or <b>ZOLTAN_SPECIAL_MALLOC_LID</b> for processor numbers, <a href="dev_lb_types.html">global IDs</a> and <a href="dev_lb_types.html">local IDs</a>, respectively.
</td>
</tr>

<tr>
<td><b>Returned Value:</b></td>

<td></td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp; int</td>

<td>1 if the allocation succeeded; 0 if it failed.</td>
</tr>

<tr>
<td VALIGN=TOP><b>Example:</b></td>

<td></td>
</tr>

<tr>
<td VALIGN=TOP></td>

<td>
<tt>
ierr = <b>Zoltan_Special_Malloc</b>(<i>zz</i>, (void **)<i>import_gid</i>,
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <i>num_import</i>,
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b>ZOLTAN_SPECIAL_MALLOC_GID</b>);
</tt>
</td>
</tr>

<tr>
<td VALIGN=TOP></td>

<td>Allocates an array with <i>num_import</i> <a href="dev_lb_types.html">global IDs</a>
and returns a pointer to the allocated space in <i>import_gid</i>.
</td>
</tr>
</table>

<p>

<!------------------------------------------------------------------------->
<hr>
<a NAME="Zoltan_Special_Free"></a>
<hr>
int <b>Zoltan_Special_Free</b>(struct <b><a href="dev_lb_structs.html#Zoltan_Struct">Zoltan_Struct</a></b>
*<i>zz</i>, void **<i>array</i>,<b> ZOLTAN_SPECIAL_MALLOC_TYPE</b> <i>type</i>);&nbsp;
<hr>
<p><b>Zoltan_Special_Free</b> frees memory allocated by <b><a href="#Zoltan_Special_Malloc">Zoltan_Special_Malloc</a></b>.
The array pointer is set to NULL upon return.
<br>&nbsp;
<table WIDTH="100%" >
<tr VALIGN=TOP>
<td VALIGN=TOP WIDTH="20%"><b>Arguments:</b></td>

<td WIDTH="80%"></td>
</tr>

<tr>
<td VALIGN=TOP><i>&nbsp;&nbsp;&nbsp; zz</i></td>

<td>The Zoltan structure currently in use.</td>
</tr>

<tr>
<td VALIGN=TOP><i>&nbsp;&nbsp;&nbsp; array</i></td>

<td>The array to be freed. Upon return, the pointer is set to NULL.</td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp;&nbsp; <i>type</i></td>

<td>The type of the array. Must be one of <b>ZOLTAN_SPECIAL_MALLOC_INT</b>,
<b>ZOLTAN_SPECIAL_MALLOC_GID</b>
or <b>ZOLTAN_SPECIAL_MALLOC_LID</b> for processor numbers, <a href="dev_lb_types.html">global IDs</a> and <a href="dev_lb_types.html">local IDs</a>, respectively.</td>
</tr>

<tr>
<td><b>Returned Value:</b></td>

<td></td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp; int</td>

<td>1 if the deallocation succeeded; 0 if it failed.</td>
</tr>

<tr>
<td VALIGN=TOP><b>Example:</b></td>

<td></td>
</tr>

<tr>
<td VALIGN=TOP></td>

<td>
<tt>
ierr = <b>Zoltan_Special_Free</b>(<i>zz</i>, (void **)<i>import_gid</i>,
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b>ZOLTAN_SPECIAL_MALLOC_GID</b>);
</tt>
</td>
</tr>

<tr>
<td VALIGN=TOP></td>

<td>Frees the <b><a href="dev_lb_types.html">global IDs</a></b>
array <i>import_gid</i> and sets it to NULL.</td>
</tr>
</table>

<br>&nbsp;
<p>
<!------------------------------------------------------------------------->
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